Pressure Gradient Controversial Calculation and Drilling Mud Profile Challenges, Case Histories Worldwide

Abstract A proposed method presented here for the proper calculation of subsurface pressure's gradient (PG), which is essential for drilling assessments, reservoirs evaluation and pore pressure prediction (PPP) modeling. The subsurface fluid density and geological compartmentalization impact to a great extent the PG. The scope of this work is to eradicate some of the unintended reservoir's pressure regime interpretations and as a consequence establish the correct mud weight equivalents in PPG (pound per gallon). The new approach is based on calculating the pressure gradient (PG) between two depth points instead of one reference point (e.g. Kelly Bushing, Derrick floor, Sub Sea etc.). A pressure "slope" is given to the calculation based on one reference point instead of proper two depth points. In the geopressured (over-pressure) system, pressure compartments exhibit hydraulic heads due the reservoir excess pressures. Drilling mud pressure should compensate for the bore hole excess pressure. Making the calculations as a result of moving the "Mud Fan" to the formation's Hydraulic Head (HH) level shows a harmony between the pressures values in PSI and mud pressure in PPG MWE, instead of the disagreement created by using the conventional conversion methods. Diagnosing the discrepancy between the pressure gradient and pressure slope trends helps avoid some of the interpretation pitfalls such as pressure regression with depth, centroid and subnormal pressure zones in clastic sediments open marine environment. It eliminates some of the pore pressure calibration modeling pitfalls as well. Moreover, it displays the right compartmentalization's pressure assessment for drilling operations, development prognosis and production purposes.